Caulking guns are used to dispense a great variety of fluid compounds including urethane, vinyl, polyester, epoxy and other plastics or resins. These different compositions have different densities. Regardless, an effective caulk gun must be capable of delivering the various compositions with uniformity. Moreover, to effect proper beading of the compounds, a caulk gun should allow a user to dispense the compounds over a range of volumetric flow rates.
Conventional economy brand caulk guns generally fail to achieve satisfactory results. These are the manual trigger-operated devices incorporating a unidirectional gripping assembly which urges a piston rod forward to eject the compound from a cartridge. Unfortunately, it is difficult to achieve the high degree of leverage often needed to dispense denser compounds. For those who can muster the necessary hand strength, the plunger drive assembly often breaks.
In order to achieve acceptable flow rates, caulking guns evolved toward complex gear-drives or pneumatic actuators. However, these are very expensive to manufacture and produce.
There remains a clear demand for an inexpensive hand-held caulking gun capable of delivering a dense composition at a high delivery volume and flow rate.
Prior art Chang U.S. Pat. No. 4,081,112 addresses the demand. The Chang caulking gun positions the trigger pivot and trigger drive grip engagement above the plunger shaft. This improvement increases the leverage obtainable by a hand operated trigger and allows delivery of the composition at a higher volume and flow rate than was previously possible in a hand-held caulking gun. Moreover, the improvement can be accomplished at no additional cost.
Related also to Chang U.S. Pat. No. 5,197,635 is a further improvement in the form of a slidable bearing assembly which allows the user to alter the leverage obtainable by squeezing the trigger. As shown in FIG. 1 of the '635 patent, the bearing assembly includes a positionable bearing bit 100 which can be fixed by means of set screw 110 anywhere along the length of the upper trigger portion 30. The lower the position, the more the leverage, and the smaller the incremental movement of the plunger shaft 55. This arrangement succeeds in uniformly dispensing different compositions of different densities over a range of volumetric flow rates. Unfortunately, adjustments cannot be made on the fly. Instead, the user must cease caulking and procure a screwdriver in order to effect the adjustment. Moreover, the adjustable bearing assembly is relatively difficult and costly to manufacture insofar as it requires machining of screw threads and the like.
Consequently, there remains a demand for a refined and less expensive adjustment feature which allows the user of a caulk dispensing gun to vary the thrust output while using the gun.